How many logical drives in 3 physical drive Raid 5

Posted on 2008-11-18
Last Modified: 2013-11-14
Installing Suse Linux on Proliant ML150 with (3) 73 gig hard drives.  Just realized it is best to allow the OS run on one logical drive and the NSS stuff run on another.  In order to have 2 logical drives both running Raid 5, I'm assuming I would need at least 6 hard drives, is that correct?  I have ordered two more so will have 5 but initially thought of doing 2 at Raid 1 and then the other 3 at Raid 5, but just wanted to make sure.  Is there better performance with allowing everything to exist on two Raid 5 logical drives as opposed to one logical Raid 1 and one logical Raid 5.  We are using 15k SAS drives so the performance should be pretty good.  Need to get an idea fast to order another drive or just wait for the two to finish the installation.

Question by:Peterson50
    LVL 4

    Accepted Solution


    with 3 x 73GB drives setup in a RAID 5, that should give you approximately 144GB of available space to use.  At this point, the entire disk array is in the RAID 5.....whether you decide to create logial drives (partitions) or not, will not affect the RAID 5.  in fact, the RAID 5 doesn't necessarily look at what logical drives you may have setup, the RAID controller just looks at it as data.  

    you can certainly add more drives to your existing RAID 5 array, that will give you more space and should increase performance a bit, as there are more disks to read/write from.  

    however, my ideal setup would be...

    OS on a RAID 1 (2 drives)
    Data on a RAID 5 (3 or more drives)

    feel free to let me know if you would like more info.  thanks

    LVL 13

    Expert Comment

    I would depend on what you're using the Raid 5 for. I would, and have, my system drive on a RAID 1 and my data ona RAID 5 array. ou should buy the 6th disk and configure it as a hotspare.
    So yes raid 1 takes the 2 drives for mirroring your system disks, and the RAID 5 will need at least 3, the 4th being a hotspare.
    If you are running any MySQL databases then I'd look at RAID 10 on your 2nd raid pack instead of raid 5 as performance for databases increase with RAID 10 apparently. RAID 10 will half your storga ethough on your 2nd pack so you woul have to utilise the 4th drive to make a 4 disk RAID 10 and have 140gb+/- storage available.
    Hope that helps

    Author Comment

    In the HP Bios it will only allow 1 logical drive for Raid 5 with 3 physical drives.  If I attempt to create 2 it automatically begins making 1 logical drive Raid 1 with the 3rd drive a separate Raid 0.  I am waiting for two additional to come to do the setup as you guys recommended.  With Netware they don't recommend create NSS paritions on a Ext3 formattted Linux so we needed to dump the one logical for at least 2 logical drives.
    But Raid 1 OS Raid 5 Data sounds good to me.  This server is migrating their Groupwise Post Office onto it.

    Thanks for the info.  
    LVL 55

    Expert Comment

    Pity they didn't but a 300 series Proliant, then they could have multiple logical disks on a single set of spindles.

    Author Comment

    Your right after speaking with HP, the ML 150 do not allow multiple logical drives on a single spindle

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